Jpn. Pat. Appln. Publication No. 2003-111341 (JP2003-111341A) discloses a fan motor (an electric fan) comprising a fan casing, a motor casing including a bearing holder, at least one ball bearing, a plurality of webs connecting a housing and the motor casing, and an impeller rotatably fixed onto a rotary shaft of the motor. The fan casing, bearing holder, motor casing, ball bearing, and plurality of webs are each made of a metal. A plurality of rolling elements are arranged via a lubricant between outer and inner races of the ball bearing. The outer race is fitted in the bearing holder. IF such an electric fan is used for a prolonged period under an environment where electromagnetic noise is generated, electric corrosion occurs in the ball bearing, causing irregularities on the track surface of the outer or inner race opposite to the rolling elements and generating noise. In the electric fan disclosed in JP2003-111341A, a grounded electromagnetic noise guard is provided in or over a suction or discharge port of the fan casing so as to prevent the electromagnetic noise from entering into the motor.
In many of such a type of electric fans, a fan casing, a motor casing, and webs are each made of an insulating resin typically by means of injection molding. Also in this case, a grounded electromagnetic noise guard is provided in or over the suction or discharge port of the fan casing so as to prevent occurrence of the electric corrosion. In such a type of electric fans, however, it is difficult to sufficiently prevent occurrence of the electric corrosion in the ball bearing although the electromagnetic noise guard is provided.